The particular frustration of living in an Edinburgh tenement is that you can often see the problem and are not allowed to touch it.
Tall sash and case windows, single glazed, in a stone wall, inside a conservation area or a listed building. Everyone knows the glass is where the heat is going. Almost nobody is permitted to replace it, and the ones who are permitted are looking at a bill that makes the rest of the flat look cheap.
So the question becomes narrower and more practical. If the glazing is fixed, what can be done on the inside of it?
The three routes heat takes out
Worth separating them, because different fixes address different routes and people tend to buy for the wrong one.
Conduction is heat passing straight through the glass. Draughts are air moving through gaps in the frame, the sash meeting rails and the case. Radiation is the cold surface of the glass pulling warmth off you directly, which is why a room can read a reasonable temperature on a thermostat and still feel unpleasant if you sit near the window.
Draught proofing tackles the second. Curtains do a little for the third. Neither does much about the first, which is where a still layer of air becomes the useful thing.
Why a trapped air gap is the mechanism that matters
Double glazing works because of the gap, not the extra pane. Air that is not moving is a poor conductor, and a sealed cavity slows heat leaving the room.
You cannot install a cavity in a listed window, but you caan create a smaller one on the room side of it. A blind built as a row of closed cells rather than a flat sheet holds air in its own structure and holds another pocket between itself and the glass when it is drawn. That is the whole principle behind 1 Click Blinds and their cellular construction, and in a single glazed room it is the most useful thing you can put in front of the window.
An honest caveat before anyone gets excited. This is a reduction, not a solution. A cellular blind in front of single glazing does not turn it into double glazing, and any supplier who implies otherwise is overselling. It takes the chill off the surface, slows the loss, and makes the space beside the window usable in January. That is a worthwhile outcome and it is not the same as a retrofit.
The listed building complication, and drilling
There is a second obstacle in older flats that is easy to overlook until the fitter arrives. Original timber frames, especially in a listed property, are not something you want to be putting screws into, and in many flats the sash boxes are original joinery.
No-screw fitting options sidestep that entirely by gripping the frame or the beading rather than fixing through it. It is worth checking your own consent conditions rather than assuming, but a non invasive fitting is generally the easier conversation with a factor or a conservation officer.
What else is worth doing at the same time
If you are already at the window, deal with the draughts while you are there. Brush seals on the meeting rail and the sash sides are cheap and take an afternoon, and they address a route that no blind touches.
For rooms where the aim is comfort rather than darkness, thermal blind options cover the same ground in a flatter fabric, which suits a living room where you want the window to look like a window.
The realistic outcome
A tenement flat with single glazing will always cost more to heat than a new build. The aim is not to close that gap, it is to make the cold half of the room usable and to stop the heating running against an open window all winter.
Do the draughts, put something insulating in front of the glass, and accept that the stonework and the sash boxes are part of what you signed up for.
